1. Field of the Invention
The present invention relates to a method of manufacturing a liquid jet recording head and, more particularly, to a method of allowing easy detection of a defect in a protective layer on a recording head.
2. Related Background Art
One of the factors determining reliability of a liquid injection recording head is the presence/absence of a defect in a protective layer formed thereon. As described in U.S. Pat. Nos. 4,536,250 and 4,602,261, if defects such as pinholes or cracks occur in such protective layers, a liquid (such as ink) enters inside the recording head through the defects to corrode electrodes and heating resistor layers. In this case, if a conductive liquid is used, an electrical short circuit is formed to prevent normal injection of the liquid. In order to minimize the defects in the protective layer or the like, materials and structures of the protective layers must be properly selected, and careful consideration must be made of the method of forming such layers.
In order to obtain a satisfactory result, a test is normally performed to detect the present/absence of defects in the protective layer during the recording head fabrication process, thereby further improving reliability of the recording head.
A typical example of a method of testing the protective layer is shown as an illustrative sectional view in FIG. 1. A portion of a recording head substrate 12 having a protective layer 15 is dipped in an ink or electrolytic solution 17 contained in a conductive vessel 16, and a voltage is applied across a bonding pad 19 of the recording head and the vessel.
If a defect is present in the protective layer 15, a current is supplied between the vessel 16 and the bonding pad through the electrolytic solution 17. By detecting the current, the presence of the protective layer 15 can be easily discriminated.
Further, the bonding pad serves as an anode, and a material of the electrolytic solution 17 is selected according to the materials of electrodes 14 and/or heating resistor layer 13 to enable the application of anodic oxidation to the electrode 14 corresponding to the defect of the protective layer 15 and/or a heat resistor layer 13.
Therefore, the repairing of the defect can be executed together with the testing at the same time.
This test method is utilized during the fabrication process before the recording head is finished, and defective heads are not fed to the subsequent process, thus providing an economical advantage in favor of fabrication process.
However, since a test electrode 18 must be attached to the bonding pad of the recording head, the bonding pad 19 may be damaged at the time of test electrode attachment, and objects such as dust may be undesirably attached to the bonding pad. Furthermore, if a plurality of electric-thermal converters are used, test electrodes must be attached to the electrodes of the respective converters, thus degrading the test efficiency.